POWER CONVERTER FOR DRIVING SWITCHED RELUCTANCE MOTOR
An upper bridge of the power converter drives a half of phase windings. A lower bridge of the power converter drives the other half of the phase windings. For example, an upper neutral point of a star-connected upper phase windings is connected to a lower neutral point of a star-connected lower phase windings via a connection switch. A current-absorbing leg absorbs a current from the upper neutral point. A current-supplying leg supplies a current to the lower neutral point. Preferably, the power converter has an asymmetric bridge mode, a dual Miller mode and an accelerated bridge mode by means of switching the connection switch, the current-absorbing leg and the current-supplying leg.
This application claims benefit under 35 U.S.C. 119 of JP2012-048906 filed on Mar. 6, 2012, the title of TRANSVERSE FLUX MACHINE APPARATUS, JP2012-85172 filed on Apr. 4, 2012, the title of POWER CONVERTER FOR DRIVING SWITCHED RELUCTANCE MOTOR, JP2012-90645 filed on Apr. 12, 2012, the title of POWER CONVERTER FOR DRIVING SWITCHED RELUCTANCE MOTOR and JP2012-95387 filed on Apr. 19, 2012, the title of POWER CONVERTER FOR DRIVING SWITCHED RELUCTANCE MOTOR, the entire content of which is incorporated herein reference.
BACKGROUND OF INVENTION1. Field of the Invention
The present invention relates to a power converter for driving a switched reluctance motor, in particular a power converter for driving a switched reluctance motor having phase windings of four or six or more than six of even number.
2. Description of the Related Art
It is known for a switched reluctance motor (SRM) to have many advantages for a variable-speed application such as a traction motor, in particular a direct-drive hub motor. However, it is known for the SRM to have drawbacks such as acoustic noise, vibration, torque ripples and a torque/weight ratio in comparison with a popular permanent magnet synchronous motor. It is known that acoustic noise, vibration, torque ripples of the SRM is reduced by increasing phase number of the SRM. However, it is not easy for the power converter to increase the phase number because of a cost of the multi-phase power converter. Many circuit topologies of power converters are proposed for SRMs.
U.S. Pat. No. 7,906,931 describes a power converter with a full-bridge per phase. However, The full-bridge power converter requires four switches per phase. A popular asymmetric bridge converter shown in
However, the voltage split four phase power converter shown in
A energy-absorber of a power converter is known. The energy-absorber has a capacitor for accumulating a demagnetizing current temporally. Typically, the energy-absorber connects each of upper diodes D2, D4 and D6 to a DC link. However, it is difficult to employ the energy absorber for the power converter of driving a large SRM because the capacitor having a large capacity under of high voltage type is large and expensive.
CITATION LIST Patent Literature
- PTL 1: U.S. Pat. No. 7,906,931
An object of the invention is to provide a simple SRM drive capable of reducing acoustic noise, vibration and torque ripples of a multi-phase SRM. Another object of the invention is to provide a simple SRM drive capable of extending a speed range of a multi-phase SRM. Another object of the invention is to provide a simple SRM drive capable of increasing a torque/weight ratio. Another object of the invention is to provide a control method of a multi-phase SRM drive having benefits mentioned above.
As for the invention, a power converter having an upper bridge and a lower bridge, which are controlled by a controller, drives a switched reluctance machine having phase windings of four or six or more than six of even number. Each upper leg of the upper bridge is connected to each upper phase windings connected to an upper neutral point. Each lower leg of the lower bridge is connected to each lower phase windings connected to an lower neutral point. The upper leg has a pair of a lower switch and an upper diode connected in series. The lower leg has a pair of an upper switch and a lower diode connected in series. The upper neutral point is connected to the lower neutral point directly or via at least one of a connection switch and a connection diode.
The power converter further has a current-adjusting circuit having at least one transistor for adjusting a neutral current flowing from the upper neutral point to the lower neutral point. Therefore, it is capable of constructing the SRM with low acoustic noise, low vibration and low torque ripples without using an expensive power converter having many power transistors or a large voltage-split capacitors. It is known that acoustic noise, vibration and torque ripples are reduced by means of increasing phase number. The power converter having essentially one switch per phase is capable of driving a six-phase SRM because the transistor of the current-adjusting circuit adjusts phase currents.
According to a preferred embodiment, the upper bridge magnetize three of odd numbered stator poles to a first magnetic polarity, and the lower phase windings magnetize three of even numbered stator poles a second magnetic polarity. Therefore, an iron loss of the six-phase SRM is reduced because the SRM of radial flux type has short flux passages
According to another preferred embodiment, one phase current of one bridge with three legs is equal to a sum of two phase currents of another bridge with three legs in an asymmetric mode. Therefore, the simple power converter can drive the six-phase SRM.
According to another preferred embodiment, one bridge supplies an increasing current of one phase and a decreasing current of another phase. The other bridge supplies an essentially constant current of another phase in the asymmetric mode. Therefore, the simple power converter without voltage split capacitors can drive the six-phase SRM.
According to another preferred embodiment, the two bridges supply each phase current having an essentially trapezoid waveforms. Therefore, the current difference between the two bridges is reduced.
According to another preferred embodiment, the two bridges supply each phase current exciting each magnetic flux having essentially half rectified sinusoidal waveforms to each phase winding. For example, the two bridges supply each phase current having essentially half rectified sinusoidal waveforms. Or, the two bridges apply to each phase voltage having essentially half rectified sinusoidal waveforms to each phase winding. Therefore, the current difference between the two bridges is reduced. Moreover, acoustic noise, vibration are reduced. Further, an iron loss of the six-phase SRM is reduced. Similarly, other known SRMs, for example a three-phase SRM, can have a low iron loss by means of employing each phase magnetic flux having essentially half rectified sinusoidal waveforms. The reason that each phase currents having half rectified sinusoidal waveforms reduce the iron loss is explained hereinafter. A predetermined average value of phase current must be supplied for one magnetization period of a SRM in order to produce a predetermined average value of a motor torque. First, the phase current is increased from zero to a predetermined value, and the phase current is decreased from the predetermined value to zero. A hysterics loss is similar to a friction loss on the mechanics. The hysterics loss is increased, when a changing speed of magnetic flux and a magnetic flux density are high. The changing speed of the magnetic flux with half rectified sinusoidal waveforms is lower than the other waveforms, when the magnetic flux density is high. Therefore, the iron loss of a SRM is reduced, when the phase currents having the half rectified sinusoidal waveforms are supplied to the SRM. In other words, changing of the magnetic flux density is easy, when the magnetic flux density is low, but the changing of the magnetic flux density is difficult, when the magnetic flux density is high. Preferably, the phase currents with half rectified sinusoidal waveforms is supplied to a SRM, when a rotation speed of the SRM is high because the iron loss of a variable-speed SRM such as the traction motor is increased very much in the high speed area. It is capable of applying the phase voltages having essentially half rectified sinusoidal waveforms to phase windings of a SRM instead of supplying the phase currents having essentially half rectified sinusoidal waveforms.
According to another preferred embodiment, the current-adjusting circuit has a current-absorbing leg connected to the upper neutral point and a current-supplying leg connected to the lower neutral point. Therefore, voltage ripples of the neutral points are reduced even though a current difference between two bridges becomes large. Therefore, the current difference between the two bridges is compensated without the voltage split capacitors.
According to another preferred embodiment, the current-absorbing leg has a current-absorbing switch for absorbing the current from the upper neutral point. The current-supplying leg has a current-supplying switch for supplying the current to the lower neutral point. Therefore, the current difference between the two bridges is compensated without the voltage split capacitors.
According to another preferred embodiment, the current-absorbing switch and the current-supplying switch are switched in accordance with either of the voltage of the neutral points or a current difference between the upper bridge and the lower bridge in the accelerated bridge mode having an essentially equal voltage of the neutral points. The switches are switched in order to reduce the ripples of the voltage of the neutral points. Therefore, the current difference between the two bridges is reduced.
According to another preferred embodiment, the upper bridge and the current-absorbing leg constitutes one Miller converter in a dual Miller mode when the connection switch is turned off. Similarly, the lower bridge and the current-supplying leg constitutes the other Miller converter in the dual Miller mode. Therefore, a torque is increased in the dual Miller mode, because a full voltage of the DC power source is applied to two Miller converters each.
According to another preferred embodiment, the dual Miller mode is selected, when either of the two bridges has a trouble. Therefore, the reliability of the power converter is improved. According to another preferred embodiment, the dual Miller mode is selected, when a rotation speed of the SRM is a high speed area. Therefore, the SRM produces a sufficient torque in the high speed area even though the back electromagnetic force (EMF) is increased in the high speed area.
According to another preferred embodiment, the magnetizing mode and the demagnetizing mode of one bridge are executed alternately with a predetermined frequency in the dual Miller mode. Therefore, the magnetization speed and the demagnetization speed are improved.
According to another preferred embodiment, changing between the magnetizing mode and the demagnetizing mode is executed by means of switching the current-supplying switch and the current-absorbing switch. Therefore, the magnetization speed and the demagnetization speed are improved.
According to another preferred embodiment, each of phase current consists of a DC current component and a sinusoidal AC current component. An amplitude of the DC current component is essentially equal to an amplitude of the sinusoidal AC current component. Therefore, an iron loss is reduced in a high speed area.
The first embodiment is explained referring to
The power converter 9 consists of an upper bridge 9A, a lower bridge 9B and a controller 300. The upper bridge 9A has a U1-phase leg 901, a V1-phase leg 903 and a W1-phase leg 905. The U1-phase leg 901 consists of an upper switch T1 and a lower diode D1 connected in series. The V1-phase leg 903 consists of an upper switch T3 and a lower diode D3 connected in series. The W1-phase leg 905 consists of an upper switch T5 and a lower diode D5 connected in series.
Upper ends of the upper switches T1, T3 and T5 are connected to a high potential DC link line 1000. Lower ends of the lower diodes D1, D3 and D5 are connected to a low potential DC link line 2000. A connection point of U1-phase leg 901 is connected to one end of the U1-phase winding 3U1. A connection point of V1-phase leg 903 is connected to one end of the V1-phase winding 3V1. A connection point of W1-phase leg 905 is connected to one end of the W1-phase winding 3W1. The other ends of the phase windings 3U1, 3V1 and 3W1 are connected to an upper neutral point NU.
The lower bridge 9B has a U2-phase leg 902, a V2-phase leg 904 and a W2-phase leg 906. The U2-phase leg 902 consists of a lower switch T2 and an upper diode D2 connected in series. The V2-phase leg 904 consists of an lower switch T4 and an upper diode D4 connected in series. The W2-phase leg 906 consists of a lower switch T6 and an upper diode D6 connected in series. Lower ends of the lower switches T2, T4 and T6 are connected to a low potential DC link line 2000. Upper ends of the upper diodes D2, D4 and D6 are connected to the high potential DC link line 1000. A connection point of U2-phase leg 902 is connected to one end of the U2-phase winding 3U2. A connection point of V2-phase leg 904 is connected to one end of the V2-phase winding 3V2. A connection point of W2-phase leg 906 is connected to one end of the W2-phase winding 3W2. The other ends of the windings 3U2, 3V2 and 3W2 are connected to a lower neutral point NL.
A star-connected upper three-phase winding 3k consists of three phase windings 3U1, 3V1 and 3W1. A star-connected lower three-phase winding 3L consists of three phase windings 3U2, 3V2 and 3W2. As shown in
A motor-driving method of power converter 9 is explained referring to
The U1-phase current IU1 flows from the leg 901 to U1-phase winding 3U1. The V1-phase current IV1 flows from the leg 903 to V1-phase winding 3V1. The W1-phase current IW1 flows from the leg 905 to W1-phase winding 3W1. The U2-phase current IU2 flows from U2-phase winding 3U2 to the leg 902. The V2-phase current IV2 flows from V2-phase winding 3V2 to the leg 904. The W2-phase current IW2 flows from W2-phase winding 3W2 to the leg 906.
In
Each real line passing on time points ‘a, r, m and n’ shows each phase current having a current amplitude I1. Each real line passing on time points ‘a, q, k and n’ shows each phase current having a current amplitude I2. Each real line passing on time points ‘a, p, j and n’ shows each phase current having a current amplitude I3. Each real line passing on time points ‘a, e, i and n’ shows each phase current having a current amplitude I4. Each real line passing on time points ‘a, b, d, e, f, h, i and n’ shows each phase current having a current amplitude I5. Each real line passing on time points ‘a, b, c, d, e, f, g, h, i and n’ shows each phase current having a current amplitude I6.
Each of phase currents IU1-IW2 increases in each current-increasing period. However, phase currents IU1-IW2 with the amplitudes I5 and I6 have a part of the constant current period in the current-increasing period from the time point ‘a’ to the time point ‘e’. Each of phase currents IU1-IW2 is mostly constant in each constant current period from the points ‘e, p, q, and r’ to the points ‘i, j, k, and m’. However, phase currents IU1-IW2 with the amplitudes I5 and 16 are not constant in the constant current period from the point ‘e’ to the time point ‘i’. Each of phase currents IU1-IW2 decreases in each current-decreasing period from the points ‘i, j, k, and m’ to the point ‘n’.
Each current-increasing periods has sixty degrees of electric angle. Each of constant-current periods has sixty degrees of electric angle. Each of current-decreasing periods has sixty degrees of electric angle. Each phase difference between adjacent two phase currents has sixty degrees of electric angle. It is important that a sum of an increasing phase current in the current-increasing period and a decreasing phase current in the current-decreasing current is equal to a constant current in the constant current period.
Phase currents IU1-IW2 is supplied by means of PWM-switching the switches T1-T6. In a first case, switches T1-T6 are PWM-switched in the current-increasing periods and the constant current periods. In a second case, switches T1-T6 are PWM-switched in the current-increasing periods and the current-decreasing periods. It should be considered that the real lines 11-16 shown in
Therefore, phase current IW2 becomes equal to a sum of phase currents IU1 and IW1 in a sub period ‘A’ from a time point t4 to a time point t5. Phase current IU1 becomes equal to a sum of phase currents IW2 and IU2 in a sub period ‘B’ from a time point t5 to a time point t6. Phase current IU2 becomes equal to a sum of phase currents IU1 and IV1 in a sub period ‘C’ from a time point t6 to a time point t1. Phase current IV1 becomes equal to a sum of phase currents IU2 and IV2 in a sub period ‘D’ from a time point t1 to a time point t2. Phase current IV2 becomes equal to a sum of phase currents IV1 and IW1 in a sub period ‘E’ from a time point t2 to a time point t3. Phase current IW1 becomes equal to a sum of phase currents IV2 and IW2 in a sub period ‘F’ from a time point t3 to a time point t4.
After all, it is considered that a voltage of the neutral points NU and NL becomes a half of DC link voltage continuously, when two of six switches T1-T6 are PWM-switched in order to accord the phase current in the constant-current period to a sum of the adjacent two phase currents in the current-increasing period and the current-decreasing period. As the result, the large capacitors C1 and C2 shown in
Accordingly, the simple power converter 9 reduces the acoustic noise, the vibration and the torque ripples largely because magnetic force between stator 2 and rotor 4 are dispersed spatially and sequentially. Further, power converter 9 supplies three phase currents simultaneously by means of PWM-switching only two of switches T1-T6. Therefore, the switching power loss of power converter 9 is reduced. Furthermore, power losses of diodes D1-D6 are reduced because the demagnetizing current flows through only one diode. In prior arts shown in
Further, a torque difference Tdif between the total torque Ttotal and the torque instruction value Tin is calculated. At next step S106, next values of phase currents IU1-IW2 are decided in accordance with torque difference Tdif and the detected phase currents IU1-IW2. At next step S108, gate voltages of switches T1-T9 are decided in accordance with next phase currents IU1-IW2. Instead of the above soft feedback operation, a hard feedback operation can be adopted.
The first arranged embodiment is explained referring to
The second arranged embodiment is explained referring to
The third arranged embodiment is explained referring to
In sub period D, phase current IW2 is equal to a sum of phase currents IU1 and IW1. In sub period E, phase current IU1 is equal to a sum of phase currents IW2 and IU2. In sub period F, phase current IU2 is equal to a sum of phase currents IU1 and IV1. In sub period A, phase current IV1 is equal to a sum of phase currents IW2 and IV2. In sub period B, phase current IV2 is equal to a sum of phase currents IV1 and IW1. In sub period C, phase current IW1 is equal to a sum of phase currents IV2 and IW2. Therefore, vibration and acoustic noise are reduced. The configurations of phase current IU1-IW2 are formed by means of PWM-switching of two phases.
Furthermore, an iron loss is reduced largely by means of employing the phase currents IU1-IW2 having the half rectified sinusoidal waveforms each. In the prior SRM-driving method, it is unknown to drive a switched reluctance motor (SRM) with phase currents having the half rectified sinusoidal waveforms each. Further, it is unknown to reduce the iron loss by means of driving the SRM with phase currents having the half rectified sinusoidal waveforms each. It is desirable to supply the phase currents with the half rectified sinusoidal waveforms to a SRM rotating in a high speed area because the iron loss is reduced largely in the high speed area. Similarly, an iron loss of the other known SRM is reduced by means of employing the phase currents with the half rectified sinusoidal waveforms. It is capable of applying phase voltages with the half rectified sinusoidal waveforms to phase windings of a SRM in order to supply phase currents having essentially half rectified sinusoidal waveforms to the phase windings of the SRM. Moreover, it is capable of modulating each phase current in accordance with non-linear magnetic characteristic of the magnet core in order to excite each phase magnetic flux having essentially half rectified sinusoidal waveforms.
A Second EmbodimentThe second embodiment is explained referring to
The connection switch T9 connects the upper neutral point NU of the upper three-phase winding 3K to the lower neutral point NL of the lower three-phase winding 3L. The current-absorbing leg 907 has a current-absorbing diode D7 and a current-absorbing switch T7 connected in series. A cathode electrode of the current-absorbing diode D7 is connected to the high potential DC link line 1000. An anode electrode of current-absorbing diode D7 is connected to upper neutral point NU. The current-absorbing switch T7 connects the upper neutral point NU to the low potential DC link line 2000.
The current-supplying leg 908 has a current-supplying switch T8 and a current-supplying diode D8 connected in series. The current-supplying switch T8 connects lower neutral point NL to the high potential DC link line 1000. An anode electrode of the current-supplying diode D8 is connected to low potential DC link line 2000. An cathode electrode of current-supplying diode D8 is connected to lower neutral point NL.
The controller 300 controls motor-driving operation of power converter 9. Controller 300 has three motor-driving modes, which are called an asymmetric bridge mode, an accelerated bridge mode and a dual Miller mode. The asymmetric bridge mode is executed, when the connection switch T9 is turned on, and the switch T7 and T8 are turned off. Therefore, the asymmetric bridge mode is same as the motor operation explained referring to
(The Accelerated Bridge Mode)
The accelerated bridge mode is explained referring to
According to the accelerated bridge mode, the current difference between upper bridge 9A and lower bridge 9B is absorbed by means of PWM-switching either of current-absorbing switch T7 and current-supplying switch T8. Therefore, the current difference between upper bridge 9A and lower bridge 9B is absorbed by either of currents I7 and I8.
The PWM-switching method can be employed instead of the one pulse method. It is considered that the difference between U2-phase current IU2 and the sum of U1-phase current IU1 and V1-phase current IV1 becomes zero by means of PWM-switching of the increasing current of V1-phase current IV1 in sub period F. However, the current difference Ix between U2-phase current (the second phase current) IU2 and the sum of U1-phase current (the first phase current) IU1 and V1-phase current (the third phase current) IV1 has large ripples in the large current operation. The controller 300 calculates the current difference Ix in accordance with the memorized map and the detected information, and supplies the current difference Ix to phase windings 3U1-3W2 by means of PWM-switching current-absorbing T7 and current-supplying switch T8. In
A feedback control method can be employed in order to control the switches T7 and T8. Switch T7 is turned on, when a sum of phase currents IU1, IV1 and IW1 is larger than a sum of phase currents IU2, IV2 and IW2. Similarly, switch T8 is turned on, when the sum of phase currents IU1, IV1 and IW1 is smaller than the sum of phase currents IU2, IV2 and IW2.
According to a preferred embodiment executing the accelerated bridge mode, the switches T7 and T8 can be switched with the feed back control method in accordance with a neutral voltage of neutral points NU and NL in order to keep the neutral voltage to a half of the DC link voltage. The switch T7 is turned on when the neutral voltage becomes higher than a half of the DC link voltage. Similarly, the switch T8 is turned on when the neutral voltage becomes lower than the half of the DC link voltage.
(The Dual Miller Mode)
The dual Miller mode of the motor-driving operation is explained referring to
The fundamental motor operation of the Miller converter is explained again referring to
According to the above dual Miller mode of the second embodiment, the magnetization mode and the demagnetization mode are executed alternately in each sub period with a predetermined frequency. Preferably, either of bridges 9A and 9B supplies both of the increasing current (magnetizing current) Ii and the decreasing current (demagnetizing current) Id. The other one of bridges 9A and 9B supplies the constant current Ic. For example, both of the increasing current Ii and the constant current Id are supplied with the PWM-switching. Thus, both of the magnetization of one phase and the demagnetization of another phase are executed well in each sub period. It is understand that each of executing times of the magnetization and the demagnetization in the dual Miller mode becomes half in comparison with a asymmetric bridge mode. However, the DC voltage applied to each of phase windings 3U1-3W2 becomes double. Accordingly, both of the magnetization speed and the demagnetization speed are not delayed by means of repeating the magnetization and the demagnetization alternately with a predetermined carrier frequency.
For example, the magnetization mode shown in
Similarly, the magnetization mode shown in
It is important that the demagnetization current is the largest at each initial time of sub periods A-F, and the magnetization current is the largest at each final time of sub periods A-F. Accordingly, controller 300 decreases a ratio Rt (=a demagnetization time Tde/a magnetization time Tma) continuously during each of sub periods A-F. Therefore, the average value of the magnetizing current and the average value of the demagnetizing current are not reduced by means of the above time-sharing operation. Thus, applying the full battery voltage applied to each phase in the dual Miller mode increases the average values of the magnetizing current and the demagnetizing current. In other words, the demagnetizing modes shown in
Switching patterns of switches T1-T9 in the above three modes are shown in
In
(A Mode-Changing Method)
The mode-changing method is explained referring to
At a next step S604, it is judged whether or not lower bridge 9B is normal. If lower bridge 9B has a trouble, only upper bridge 9A is driven as the Miller converter at a step S606. In other words, the magnetization current is supplied from one of three upper switches T1, T3 and T5 to the switch T7 through the phase windings 3U1, 3V1 and 3W1. Next, it is judged whether or not both of upper bridge 9A and lower bridge 9B are normal at a step 608. If both of upper bridge 9A and lower bridge 9B have a trouble each, bridges 9A and 9B are stopped, and the controller 300 outputs the alarm signal at a step 614.
Next, it is judged whether or not a detected rotor speed Nr is higher than a predetermined high threshold value Nrthh at a step S610. When the rotor speed Nr is higher than the high threshold value Nrthh, the dual Miller mode is executed at a step S612. The dual Miller mode is excellent for driving the SRM in the high-speed area because a full-scale of battery voltage is applied to each phase winding 3U1-3W2 each. In the high-speed area, phase currents IU1-IW2 of the sufficient value are supplied to phase windings 3U1-3W2 even though the back EMF is increased.
Next, it is judged whether or not a detected rotor speed Nr is higher than a predetermined high threshold value Nrthh at a step S610. When the rotor speed Nr is higher than the high threshold value Nrthh, the dual Miller mode is selected at a step S612. Further, it is judged whether or not a detected motor rotation speed Nr is lower than a predetermined low threshold value NrthL at a step S616. When the speed Nr is lower than the low threshold value NrthL, it is judged whether or not an instruction value of the motor torque Ti is larger than a predetermined value Tth as a step S618. When the instruction value of the motor torque Ti is not larger than the predetermined value Tth, the asymmetric bridge mode is executed at a step S620. When the instruction value of the motor torque Ti is larger than the predetermined value Tth, the accelerated bridge mode is executed at a step S622. The asymmetric bridge mode is excellent in the low speed area. The accelerated bridge mode is excellent in the low-speed-high-torque area.
A First Arranged EmbodimentThe first arranged embodiment is explained referring to
The configurations of phase currents IU1-IW2 are enable, when the dual-Miller mode is executed, because the sum of the first phase current and the third phase current is not equal to the second phase current. The configurations of phase currents IU1-IW2 shown in
In the prior SRM-driving method, it is unknown to drive a switched reluctance motor (SRM) with phase currents having a sum of a DC current and a sinusoidal AC current. Further, it is unknown to reduce the iron loss by means of driving the SRM in the high speed area with a sum of a DC current and a sinusoidal AC current. The other SRM, for example the three-phase SRM, can be used the above SRM-driving method employing the sum of the DC current and the sinusoidal AC current.
A Second Arranged EmbodimentThe second arranged embodiment is explained referring to
The third arranged embodiment is explained referring to
The fourth arranged embodiment is explained referring to
The fifth arranged embodiment is explained referring to
The sixth arranged embodiment is explained referring to
The motor operation of the three-phase SRM is essentially same as the motor operation of the second embodiment shown in
Another difference between the three-phase operation shown in
The seventh arranged embodiment is explained referring to
The eighth arranged embodiment is explained referring to
Power converters 9 explained above is capable of driving the three-phase SRM shown in
The third embodiment is explained referring to
Four-phase power converter 9 shown in
The first arranged embodiment is explained referring to
Six-phase power converters 9, which means a power converter having six legs connected to the neutral point, has been explained in the first embodiment and the second embodiment. Four-phase power converters 9 having four legs connected to the neutral point has been explained in the third embodiment. It is easily considered for a skilled engineer that the power converter 9 is capable of having more phases (more legs connected to the neutral point) in order to drive a SRM with more-phases. Further, it is considered easily that power converter 9 is capable of magnetizing a switched reluctance generator (SRG). Furthermore, power converter 9 can include the energy-absorber having a capacitor or a reactor in order to accumulate a residual magnetic energy temporarily. For example, it is capable that anode electrodes of lower diodes D1, D3, D5 can be connected to a capacitor capable of absorbing a current from the DC link line 2000 via a reactor or a switch. Similarly, cathode electrodes of upper diodes D2, D4, D6 are connected to a capacitor capable of supplying a current to the DC link line 1000 via a reactor or a switch. Further, diodes D1-D9 of power converter 9 can include transistors having essentially same rectification operation. Or, it is capable to connect transistors to diodes D1-D9 in parallel in order to reduce the diode power loss.
Claims
1. A power converter for driving a switched reluctance motor having four or six or more than six phase windings (3U1-3W2) of even number, wherein:
- the power converter has an upper bridge (9A), a lower bridge (9B) and a controller (300); the upper bridge (9A) has two or three or more than three of upper legs (901, 903, 905) connected to two or three or more than three of upper phase windings (3U1, 3V1, 3W1) connected to an upper neutral point (NU) each; the lower bridge (9B) has two or three or more than three of lower legs (902, 904, 906) connected to two or three or three more than three of lower phase windings (3U2, 3V2, 3W2) connected to a lower neutral point (NL) each; each of the upper legs (901, 903, 905) has a pair of a lower switch (T1, T3, T5) and an upper diode (D1, D3, D5) connected in series and supplies each of phase currents (IU1, IV1, IW1) to each of the upper phase windings (3U1, 3V1, 3W1); each of the lower legs (902, 904, 906) has a pair of an upper switch (T2, T4, T6) and a lower diode (D2, D4, D6) connected in series and receives each of phase currents (IU2, IV2, IW2) from each of the lower phase windings (3U1, 3V1, 3W1); the upper neutral point (NU) is connected to the lower neutral point (NL) directly or via at least one of a connection switch (T9) and a connection diode (D9); and the power converter further has a current-adjusting circuit (9A, 9B, 300, T7-T9) including at least one switch (T1-T9) for reducing voltage ripples of the two neutral points (NU, NL) connected to each other.
2. The power converter according to claim 1, wherein the switched reluctance machine of radial flux type has three of the upper phase windings (3U1, 3V1, 3W1) and three of the lower phase windings (3U2, 3V2, 3W2);
- each of the upper phase windings (3U1, 3V1, 3W1) magnetizes each of odd numbered stator poles (20) of the switched reluctance machine to a first magnetic polarity; and
- each of the lower phase windings (3U2, 3V2, 3W2) magnetizes each of even numbered stator poles (20) of the switched reluctance machine to a second magnetic polarity.
3. The power converter according to claim 1, wherein the controller (900) has an asymmetric mode connecting the upper neutral point (NU) to the lower neutral point (NL);
- the current-adjusting circuit is constituted by the upper bridge (9A), the lower bridge (9B) and the controller (300);
- the upper bridge (9A) having three of odd numbered legs (901, 903, 905) supplies one phase current (IU1, IV1, IW1) being essentially equal to a sum of two phase currents (IU2, IV2, IW2) of the lower bridge (9B) in each of odd numbered sub periods (A, C, E) of the asymmetric mode; and
- the lower bridge (9A) having three of even numbered legs (902, 904, 906) supplies one phase current (IU2, IV2, IW2) being essentially equal to a sum of two phase currents (IU1, IV1, IW1) of the upper bridge (9B) in each of even numbered sub periods (B, D, F) of the asymmetric mode.
4. The power converter according to claim 3, wherein the upper bridge (9A) supplies an increasing current of one phase and a decreasing current of another phase in each of the even numbered sub periods (B, D, F) of the asymmetric mode;
- the lower bridge (9B) supplies an essentially constant current of another phase in each of the even numbered sub periods (B, D, F) of the asymmetric mode;
- the upper bridge (9A) supplies an essentially constant current of one phase in each of the odd numbered sub periods (A, C, E) of the asymmetric mode; and
- the lower bridge (9B) supplies an increasing current of another phase and a decreasing current of another phase in each of the odd numbered sub periods (A, C, E) of the asymmetric mode.
5. The power converter according to claim 1, wherein the upper bridge (9A) and the lower bridge (9B) supply each phase current with half rectified sinusoidal waveforms each to each phase winding (3U1, 3V1, 3W1, 3U2, 3V2, 3W2).
6. The power converter according to claim 1, wherein the current-adjusting circuit has a current-absorbing leg (907) and a current-supplying leg (908);
- the current-absorbing leg (907) connected to the upper neutral point (NU) absorbs a current from the upper neutral point (NU) in order to reduce ripples of a voltage of the upper neutral point (NU); and
- the current-supplying leg (908) connected to the lower neutral point (NL) supplies a current to the lower neutral point (NL) in order to reduce ripples of a voltage of the lower neutral point (NL).
7. The power converter according to claim 6, wherein the current-absorbing leg (907) has a current-absorbing switch (T7) for absorbing the current from the upper neutral point (NU); and
- the current-supplying leg (908) has a current-supplying switch (T8) for supplying the current to the lower neutral point (NL).
8. The power converter according to claim 7, wherein the controller (300) has an accelerated bridge mode having an essentially equal voltage of the neutral points (NU, NL); and
- the controller (300) switches the current-absorbing switch (T7) and the current-supplying switch (T8) in accordance with either of the voltage of the neutral points (NU, NL) or a current difference between the upper bridge (9A) and the lower bridge (9B) in the accelerated bridge mode in order to reduce the ripples of the voltage of the neutral points (NU, NL).
9. The power converter according to claim 1, wherein the controller (300) has a dual Miller mode when the connection switch (T9) is turned off; the current-absorbing leg (907) has a current-absorbing switch (T7) and a current-absorbing diode (D7) connected in series;
- the current-adjusting circuit has a current-absorbing leg (907) and a current-supplying leg (908);
- the current-supplying leg (908) has a current-supplying switch (T8) and a current-supplying diode (D8) connected in series;
- the upper bridge (9A) and the current-absorbing leg (907) constitute one Miller converter in the dual Miller mode; and
- the lower bridge (9B) and the current-supplying leg (908) constitutes another Miller converter in the dual Miller mode.
10. The power converter according to claim 9, wherein the controller (300) selects the dual Miller mode, when the controller (300) detects a trouble of either of the upper bridge (9A) and the lower bridge (9B).
11. The power converter according to claim 9, wherein the controller (300) selects the dual Miller mode, when a detected rotation speed of the switched reluctance machine is higher than a predetermined value.
12. The power converter according to claim 9, wherein the controller (300) has both of a magnetizing mode for supplying a magnetizing current to one of the odd numbered windings (3U1, 3V1, 3W1) and a demagnetizing mode for supplying a demagnetizing current to another of the odd numbered windings (3U1, 3V1, 3W1) in the dual Miller mode;
- the controller (300) has both of another magnetizing mode for supplying another magnetizing current to one of the even numbered windings (3U2, 3V2, 3W2) and another demagnetizing mode for supplying another demagnetizing current to another of the even numbered windings (3U2, 3V2, 3W2) in the dual Miller mode; and
- the controller (300) executes the magnetizing mode and the demagnetizing mode alternately with a predetermined frequency.
13. The power converter according to claim 12, wherein the controller (300) executes the magnetizing mode and the demagnetizing mode of one of the two Miller converters alternately by means of switching the current-absorbing switch (T7) with a predetermined frequency; and
- the controller (300) executes the magnetizing mode and the demagnetizing mode of another of the two Miller converters alternately by means of switching the current-supplying switch (T8) with a predetermined frequency.
14. The power converter according to claim 9, wherein the controller (300) has a silent drive mode supplying phase currents having a sum of a DC current component and a sinusoidal AC current component each; and
- an amplitude of the DC current component is essentially equal to an amplitude of the sinusoidal AC current component.
Type: Application
Filed: Apr 21, 2012
Publication Date: Sep 12, 2013
Inventor: Shouichi Tanaka (Nagoya)
Application Number: 13/452,835
International Classification: H02P 6/14 (20060101);